Palladium/platinum alloy

ABSTRACT

An alloy comprising 65-85% palladium by weight, 5-15% nickel by weight, and 5-20% platinum by weight is provided. The alloy may optionally contain up to 15% by weight a platinum group metal selected from osmium, ruthenium, rhodium, and iridium. The alloy exhibits a unique combination of strength, ductility, density, and opacity suitable for use as wire, tube, sheet, or foil products.

FIELD OF INVENTION

[0001] This invention relates generally to alloys and more specifically to palladium/platinum alloys.

BACKGROUND OF INVENTION

[0002] Specialized alloys for use in various applications have been the target of research for centuries. More recently, some of these specific applications include dental and orthodontal uses, general medical applications including stents, jewelry, industrial uses such as catalytic-capturing nets and related catalysis applications, pinning wires for investment casting, and electrodes for use in ignition products such as spark plugs. Each of these various applications requires alloys having specific physical, mechanical and chemical properties.

[0003] In the case of many surgical applications, such as stents, certain opacity requirements must be met so that during placement of the stent radiographic means can be employed to insure proper placement, and in some cases alignment, of the stent. In addition to radiopacity, biocompatibility and corrosion resistance are important requirements for the materials used to make stents. High strength is also required or desirable in many stent applications. These attributes would also apply, for the most part, to wires and materials used in braces in the orthodontal field. Biocompatibility, strength, and good corrosion resistance in a slightly acidic environment, are all required of an alloy used in the orthodontal field.

[0004] Another common application of specialized alloys includes ignition tips for spark plugs. In such applications, the materials must be able to be fabricated to the base metal cores (such as welding). In addition, the alloys must have excellent corrosion and erosion resistance to the harsh environments of a combustion chamber and they must possess good electrical properties such as low thermionic work function. It would be desirable for this application to meet all properties without compromise.

[0005] The high melting point characteristics of platinum group metals and their excellent resistance to oxidation makes them also useful for specialized industrial applications such as pinning wires or the devices used to position complexed cavities, such as cooling passages during the “lost wax” investment casting process.

[0006] Many platinum group metal alloys also offer catalytic behaviors desired for automotive exhaust applications as well as in the production of nitrates and nitric acid.

[0007] An improved alloy would provide many of these attributes and do so over large temperature ranges. Such an alloy would encompass many of the above-described physical properties so that the alloy could be used in many different applications.

BRIEF SUMMARY OF INVENTION

[0008] The present invention provides an alloy containing 65-85% palladium by weight, 5-15% nickel by weight, and 5-20% platinum by weight. The alloy may optionally include, up to 15% by weight, an additional platinum group element selected from osmium, ruthenium, rhodium, iridium, or combinations thereof. Preferred among these are ruthenium, rhodium, and iridium. The alloy exhibits a unique combination of strength, ductility, density, and opacity suitable for use as wire, tube, sheet, or foil products in the applications referred to above.

BRIEF DESCRIPTION OF THE DRAWING

[0009]FIG. 1 is a strain hardening curve for an alloy according to the present invention;

[0010]FIG. 2 is an annealing curve for an alloy of FIG. 1;

[0011]FIG. 3 is a strain hardening curve for a second alloy according to the present invention;

[0012]FIG. 4 is an annealing curve for the alloy of FIG. 3;

[0013]FIG. 5 is a strain hardening curve for yet a third alloy according to the present invention; and

[0014]FIG. 6 is an annealing curve for the alloy of FIG. 5.

DETAILED DESCRIPTION OF INVENTION

[0015] The present invention provides an alloy containing 65-85% palladium by weight, 5-15% nickel by weight, and 5-20% platinum by weight. The alloy may optionally include, up to 15% by weight, an additional platinum group element selected from osmium, ruthenium, rhodium, iridium, or combinations thereof. Preferred among these are ruthenium, rhodium, and iridium. A preferred alloy contains nickel at 10-15% by weight. This alloy demonstrates physical properties which include high strength, ductility, density, and opacity, and can be manufactured into wire, tube, sheet, and foil products. Moreover, the alloy exhibits a wide range of mechanical properties and corrosion/oxidation resistance which makes it suitable for a wide range of applications including medical and orthodontal applications, ignition electrodes, pinning wires, and catalytic materials.

[0016] The alloy of the present invention has density and opacity properties between those typical of stainless steel alloys and previously well-known binary platinum alloys. Previously there were no available alloy systems with comparable mechanical properties in this desirable mid-range of density and opacity. In other words, selection of application by mechanical properties would result in density and opacity that were too low for some applications in stainless steel or correspondingly too high for Pt binary alloys. For example, in certain biomedical applications opacity of 316 stainless steel may be inadequate to readily distinguish location within the body as it does not adequately contrast with various body tissues. On the other hand, use of conventional platinum binary alloys may result in excessive x-ray absorption resulting in an indication of extreme brightness making resolution of adjacent body tissue difficult.

[0017] Further, in addition to medical applications where specific opacity is required, the alloy also covers a wide range of tensile strengths and ductilities compared to prior palladium based alloys, expanding useful applications to dental devices, ignition devices such as spark plug electrodes, and pinning wires for investment castings.

[0018] The alloys of the present invention can be hot or cold worked into convenient forms such as tube, wire, sheet, or foil capable of demonstrating a wide range of mechanical properties depending on particular heat treatment conditions. Table 1 presents a comparison of the density of a typical stainless steel, a typical binary platinum group metal alloy, and the alloy of the present invention. TABLE 1 MATERIAL DENSITY 316 Stainless Steel  8.03 g/cc Typical Pt/Ir Alloys 21.45-21.8 g/cc Alloy according to present invention   12-12.5 g/cc

[0019] In addition to having desirable intermediate density, the alloy of the present invention demonstrates good workability and can be readily manufactured utilizing conventional hot/cold forming processes and can be used to produce tube, wire, sheet, and foil products. The alloy can be selectively strain hardened, stress relieved, or annealed to achieve a wide range of tensile properties from high tensile strength to high tensile ductility. In general, by manipulating the alloy through a series of steps, alternating between annealing and straining (through, for example, cold working and heat treating), the desired properties can be achieved. This aspect is demonstrated in more detail in the examples below.

[0020] One advantage to the alloy of the present invention is that it provides a wide range of mechanical properties and corrosion/oxidation resistance suitable for use in many applications, including medical applications, orthodontal applications, ignition electrodes (spark plugs) and pinning wires.

EXAMPLES Example 1

[0021] In this example, an alloy according to the invention was produced and comprised 80 wt % palladium, 10 wt % nickel, and 10 wt % platinum. Its density was 12.1 g/cc and it demonstrated the tensile properties as shown in FIGS. 1 and 2. FIG. 1 illustrates the strain hardening curve for this alloy and shows the tensile properties as a function of cold work reduction (wire cross-section reduction). FIG. 2 illustrates the annealing curve for this alloy and shows the tensile properties as a function of annealing temperature.

[0022] More specifically, FIG. 1 shows that the strength of the alloy can be manipulated through known techniques such as cold working (rolling in the case of a sheet, drawing in the case of wire or tube products). As the cross-sectional area is reduced, the strength increases. As the rolling continues and area reduction continues (shown along the abscissa), the ultimate tensile strength increases, as shown along the left ordinate. Conversely, as the rolling process progresses, the tensile elongation decreases, as shown by the elongation percentage marked along the right ordinate of FIG. 1. The tensile elongation decreases rather quickly during the first 25% area reduction, and then levels out, somewhat asymptotically, thereafter.

[0023]FIG. 2 illustrates, however, for the same alloy, cold worked 75-80%, that annealing can reverse the events shown in FIG. 1. FIG. 2 illustrates what happens to ultimate tensile strength and tensile elongation during annealing. The annealing temperature is shown along the abscissa for a 30 minute holding time. As annealing temperature increases, the ultimate tensile strength decreases, most dramatically between approximately 1000° F. and approximately 1200° F. This region covers the recrystallization temperature of the alloy. FIG. 2 also illustrates that the tensile elongation increases with annealing temperature, most notably over this same region.

[0024] Thus, by using FIGS. 1 and 2 together, one can achieve nearly any balance between the properties of the alloy of the present invention simply by working and annealing the alloy to a desired state. This fact is illustrated by the following.

[0025] The alloy of this example, comprising 80 wt % palladium, 10 wt % nickel, and 10 wt % platinum, was formed into a sheet using known methods and the tensile properties of the sheet made of this alloy were tested as the material was rolled and annealed through a series of steps. Table 2 presents the results of the test. In each step, the percentage reduction in cross section is with respect to the original cross section. TABLE 2 SHEET Condition at which Ultimate Tensile Strength Tensile measurement made (UTS) in ksi Elongation (%) As rolled 50% cross section 98.5  4% reduction Annealed after 50% cross 65 65% section reduction As rolled 80% cross section 115  2% reduction Annealed after 80% cross 63.5 70% section reduction As rolled 88% cross section 119 1.8%  reduction Annealed after 88% cross 62.5 70% section reduction

[0026] This example shows that with increased cross section reduction by cold rolling (50%-80%-88%), the tensile strength continues to increase. After annealing at each % cold work condition the sheet tensile strength returned to the same soft condition of 62-65 ksi UTS and 65-70% elongation. Thus, the sheet can be manipulated to possess the desired properties at any thickness. In other words, the sheet can be rolled and/or heat treated to the point where the desired thickness is achieved and the desired mechanical properties are attained.

EXAMPLE 2

[0027] In this example, an alloy according to the present invention comprising 75 wt % palladium, 10 wt % nickel, and 15 wt % platinum was used. Its density was 12.41 g/cc, which exceeded the density of the alloy of Example 1. This alloy was drawn into a wire and the tensile properties were examined and provided in a graphical format. FIG. 3 illustrates the strain hardening curve for this alloy and shows the tensile properties as a function of cold work reduction (wire cross-section reduction). FIG. 4 illustrates the annealing curve for this alloy and shows the tensile properties as a function of annealing temperature. The wire used to generate the data presented in FIG. 4 had a diameter of 0.057 inches and represented 75-80% cross section reduction.

[0028] As in Example 1, FIG. 3 shows that as the wire was drawn, its tensile elongation reduced rapidly over the first approximately 25% of area reduction, but that the ultimate tensile strength increased throughout the drawing process. FIG. 4 shows that as annealing temperature increases, the ultimate tensile strength decreases rather linearly, until the annealing temperature used is approximately 1100° F., at which point the ultimate tensile strength drops rather dramatically, again because the recrystallization temperature is approximately 1100° F. As was the case in Example 1 for the sheet, tensile elongation can be increased by annealing at higher and higher temperatures, up to about 1200° F., at which point tensile elongation levels out. Moreover, and as was discussed in the case of Example 1, the desired properties of the wire can be manipulated through a series of drawings and annealing steps to achieve a resultant wire which has the desired diameter and stength.

[0029] The alloy of Example 2, comprising 75 wt % palladium, 10 wt % nickel, and 15 wt % platinum, was formed into a wire and the tensile properties of the wire made of this alloy were tested as the material was drawn and annealed through a series of steps. Table 3 presents the steps and the results of the test. In each step, the percentage reduction in cross section is with respect to the original cross section. TABLE 3 WIRE Ductility Condition at which Ultimate Tensile Strength in Tensile measurement made (UTS) in ksi Elongation (%) As drawn 75% cross section 130 2.5% reduction As drawn 96% cross section 140 1.8% reduction Annealed to full  70  60% recrystallization (after 96% reduction)

[0030] This example shows that after each drawing occurred, and thus as the wire cross section was reduced, the tensile strength was increased and elongation reduced. Following heat treatment, tensile strength was returned to the “soft” condition and tensile elongation was restored to 60%. Thus, the wire can be produced to achieve a wide range of tensile strength and ductility conditions.

EXAMPLE 3

[0031] The alloy of this example comprised 75 wt % palladium, 10 wt % nickel, 10 wt % platinum, and 5 wt % iridium. This alloy had a density of 12.42 g/cc. FIG. 5 illustrates the strain hardening curve for this alloy and shows the tensile properties as a function of cold work reduction (wire cross-section reduction). FIG. 6 illustrates the annealing curve for this alloy and shows the tensile properties as a function of annealing temperature. The wire used to generate the data presented in FIG. 6 had a diameter of 0.057 inches and represented 75-80% cross-section reduction.

[0032] As in the above examples, the curves show that ultimate tensile strength and tensile elongation can both be manipulated by varying area reduction and heat treatment. As discussed above in the first two examples, the variables can be manipulated to yield an alloy product having the desired mechanical properties.

[0033] The alloy of this example, comprising 75 wt % palladium, 10 wt % nickel, 10 wt % platinum, and 5 wt % iridium, was formed into a tube using known methods of deep draw and mandrel/plug drawing techniques using intermediate anneals in non-oxidizing environments (excluding hydrogen as an environment). The tube tested had an outside diameter of 0.070″ and a wall thickness of 0.0026″. The tensile properties of the tube made of this alloy were tested as the material was drawn and annealed at 1200° F. through a series of steps. Table 4 presents the steps and the results of the test. TABLE 4 TUBE Condition at which Ultimate Tensile Strength Ductility in Ten- measurement made (UTS) in ksi sile Elongation (%) As drawn 75% area 137  3% reduction Fully annealed after 75%  80 45% area reduction

[0034] The results show that after the tube is drawn and the ultimate tensile strength increases, the annealing process returns the tensile elongation to a higher value, namely from 3% to 45%. This is consistent with the above examples and the discussion related to the manipulation of these steps to achieve the final product having the desired characteristics for sheet and wire as well.

[0035] For applications such as medical stents where deployment involves ready expansion of the device, whether by balloon inflation or self expanding architectures, one might choose to heat treat the alloy for minimum strength and maximum ductility. Then as the device is expanded to its desired application, the induced strain caused by the expansion would increase the alloy strength and resist return to the original dimensional state by the forces of constricting blood vessels or other body lumen.

[0036] For applications where initial strength is desired such as pinning wires where small diameter wires are required to support the weight of ceramic inserts during investment casting, final heat treatment may not be required.

[0037] Correspondingly, for intermediate applications, such as the knitting or weaving of catalytic gauze wire, an intermediate combination of strength and ductility is required. In such a case, a stress relief or partial anneal conditioning step may be preferred.

[0038] It should also be noted that a part of the invention includes the selective use of varying nickel amounts with various amounts of different platinum group metals. This selectivity can be used to modify the exact performance of the resultant alloy, all within the ranges included in the present invention. For example, by slightly increasing nickel and/or Pd (at the expense of Pt and/or Ir), one sees a decrease in density and a reduction in opacity. Conversely, where reduced density and opacity are not particularly relevant, such as for use in jewelry, one would decrease palladium and/or nickel with respect to platinum.

[0039] Although the present invention has been particularly described in conjunction with specific preferred embodiments, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications, and variations as falling within the true scope and spirit of the present invention. 

What is claimed:
 1. An alloy comprising: 65-85% palladium by weight; 5-15% nickel by weight; and 5-20% platinum by weight.
 2. The alloy of claim 1 wherein said nickel is present at 10-15% by weight.
 3. The alloy of claim 1 further comprising, up to 15% by weight, a platinum group metal selected from the group consisting of osmium, ruthenium, rhodium, and iridium.
 4. The alloy of claim 2 wherein said platinum group metal is selected from the group consisting of iridium, rhodium, and ruthenium.
 5. The alloy of claim 1 wherein said alloy comprises 80% palladium by weight, 10% nickel by weight, and 10% platinum by weight.
 6. The alloy of claim 1 wherein said alloy comprises 75% palladium by weight, 10% nickel by weight, and 15% platinum by weight.
 7. The alloy of claim 3 wherein said alloy comprises 75% palladium by weight, 10% nickel by weight, 10% platinum by weight, and 5% iridium by weight.
 8. An alloy comprising: 65-85% palladium by weight; 5-15% nickel by weight; 5-20% platinum by weight; and up to 15% by weight a platinum group metal selected from the group consisting of osmium, ruthenium, rhodium, and iridium.
 9. The alloy of claim 8 wherein said nickel is present at 10-15% by weight. 